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<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button id="btn">按钮</button>
    <script>
        var id="1001"
        var btn = document.getElementById("btn")
        btn.onclick = function(){
            setTimeout(function(){   // window.setTimeout
                console.log(this.id);   // 1001 
            },1000)
        }
    </script>
</body>
</html>